Gain-control circuits for repeaters



April 13 1926. 1,580,624

H. NYQUIST ET AL GAIN CONTROL CI IRCUITS FOR REPEATERS Filed Sept. 12. 1.923

W A TTORNE Y PatentedApr. 13, 1926.

UNITED STATES PATENT OFFICE.

HARRY NYQUIST, OF ELMHURST, NEW YORK, LEWIS L. BOUTON, OF LEONIA, NEW

JERSEY, AND HUGH F. SHOE-FSTALL, OF NEW YORK, N. Y., ASSIGNORS T0 AMERI- CAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

GAIN-CONTROL CIRCUITS FOR REPEATERS.

Application filed September 12, 1923. Serial No. 662,284.

To all whom it may concern:

Be .it known that we, HARRY NY UIs'r,

LEWIS L. BOUTON, and HUGH F. SHOFFSTALL,

residing at Elmhurst, Leonia, and New York, in the counties of Queens, Bergen, and Bronx and States of New York, New Jersey, and New York, respectively have invented certain Improvements in (lain-Control Circuits for Repeaters, of which the fol lowing is a specification.

This invention relates to transmission circuits and more particularly to transmission circuits including repeaters, such, for example, as two-way two-element repeaters.

One of the principal objects of the inven tion is to provide suitable methods and means for maintaining substantially constant the transmission equivalent of a circuit regardless of variations in the conditions affecting the electrical characteristics of the circuit. In general, the transmission equivalent of a circuit varies, due to a. num ber of difl erent causes. One of the main causes of variation is due to variations in the resistance, due to temperature changes.

Among other causes may be enumerated variations in capacity, inductance, or other electrical characteristics of the line and also variations in the potential of repeater batteries common to repeaters ,in both sides of the circuit. Variations may also be caused by changes in insulation or in structure of ap )aratus associated with the lines;

be present invention contemplates eliminating these difficulties by automatically varying some adjustable element of the transmission circuit to compensate for the variation introduced .in said circuit. The objects of the invention are secured as herein dis closed by causing a. suitable translating apparatus to be actuated in'accordance with changes in the electrical character of some one of a group of circuits. The remaining circuits of the group are then adjusted to compensate for the changes indicated by the first circuit. More specifically, these results are accomplished by arranging the first mentioned or pilot circuit in one element of a Wheatstone brid e arrangement, so that variable currents wi l flow through the bridge With variations in the conductivity of the pilot circuit. Apparatus in the bridge cir-- cuit is so arran d as to respond to the currents flow ng t ereln to control an automatic switch for adjusting a transmission varying device associated with the transmiss1on circuit. The transmission varying device of this invention comprisesan artificial line including a plurality of series and shunt elements and associated with the input circuits of the repeaters. The actuation of the automatic switch will operate to cut into the circuit more or less of the artificial line elements and thus vary the repeater gain to compensate for changes or variations in the transmission equivalent of the circuit. Other objects and features of the invention will Winding transformers 21 and 22, and the balancing networks N and N The input of amplifier A, is bridged across the midpoints of windings 21 by means of-conductors 23, 24 and 25, 26. Associated with these conductors is the transmission varying device, comprising the artificial line N The artificial line N includes the conductors 62, 63, 64 and 65, which interconnect conductors 23, 24, and 25, 26. Conductors 62, 63,64 and include the series resistances '1 's, '55 1, 3, 5, 7J1 1 e7 5, r,, r',, r',, r',,, and r', in the manner shown. Included in a circuit whereby they may be bridged, across conductors 62 and 63 at points 60, and 61 are the resistances 1' 7' 1' r, and 12,. p The relays 1, 3, 5, 7 and 9, 8, 6, 4, 2 are provided to control shunts about these resistances whereby moreor less of the first group of'resistances may be included in series in both sides of the input circuit of amplifier A and more or less of both groups of resistances may be connected in shunt across said circuit. Accordingly, by operating certain of these relays the elements of artificial line N may be varied to control the gain of the repeater circuit of amplifier A and thus compensate for variations in the transmission equivalent of the line L,.

The input of-amplifier A is bridged across the midpoints of windings 22 by means of conductors 27, 28 and 29, 70. Associated with these conductors is the transmission varying device comprising the artificial line N The artificial line N 4 is identically the same as artificial line N and its elements may be cut in or out of the input circuit of amplifier A by means of shunt paths controlled by the lower contacts of relays 1 to 9 inclusive to control amplifier A to compensate for changes in the transmission equivalent of line L,. The variations of the elements in line N to control the efiective gain of amplifier A not only compensates for variations in line L but also in line L andthus holds the transmission constant in the direction from L to L Network N associated with amplifier A holds the transmission constant in the direction from L to L, in a similar manner. As artificial line N, is the same as artificial line N no further description thereof will be given.

The relays 1,3, 5, 7 and 9, 8, 6, 4, 2 are controlled over conductors 1, 3, 5, 7 and 9, '8, 6, 4, 2 by a series of master relays 50 to 30 inclusive. The master relays are controlled by the contacts 50' to 30 inclusive by means of the switch S, which in turn is controlled by the pilot wire circuit L The pilot wire circuit L is included in the same cable and is subject to the same conditions as the line, such as line sections L and L the variations in which are to be compensated for. The pilot circuit L is included in one branch of a Wheatstone bridge in which the resistance R which may be equivalent to the average resistance of the pilot circuit L forms a second branch. Resistances R and R respectively constitute the third and fourth branches. In circuit'with the pilot circuit L and the resistance R is an adjustable resistance 11,, for balancing the bridge, said resistance being controlled by a wiper S carried by the switchSQ The Wiper S is included in the bridge circuit of the WVheatstone balance, the said circuit also including a polarized relay 93 which controls the operation of the switch S through the medium of the stepping magnets 94 and 95 and the holding magnets 96 and 97. Assuming that a change takes place in the resistance of the pilot circuit L due to a changein temperature or other cause, the Wheatstone bridge is unbalanced and a current flows over the bridge circuit through the winding of the polarized relay 93 and over the wiper S If the resistance of the circuit L is increased, this current is insuch a direction as to throw the armature of the polarized relay 93 to the left, as shown in the drawing, thereby completing a circuit from battery 99, through the winding and over the back con-' tact of buzzer relay 100, over the leftfhand contact of polarized relay 93, winding of stepping magnet 94 and winding of release magnet 97. The release magnet 97 draws the pawl carried by the armature of stepping magnet 95 from engagement with the corresponding ratchet wheel and the stepping magnet 94 operates its ratchet wheel step by step with each interruption of the circuit by the buzzer relay 100 to rotate the wiper S in counter-clock-wise direction. The division of the resistance R between the arms of the bridge including the pilot circuit L and the resistance R is thereby changed until the Wheatstone bridge is again balanced. This action moves the switch S in a counter-clock-wise direction, thereby affecting the master relays and the relays controlling the artificial line N to increase the gain of the repeater in the direction from L to L as will be pointed out in detail hereinafter. If the change in the condition of the pilot circuit L is of such nature as to cause a reduction of the resistance, the current flows through the windings of the polarized relay 93 in the opposite'direction and a circuit is closed through the buzzer relay 100, stepping magnet 95 and release magnet 96 to step the switch S in a clockwise direction, thereby affecting the master relays and the artificial line relays to decrease the gain of the repeater in the direction from line L, to L When the key K is operated, ground will be. applied over its up er contact to conductor 66 and through t e winding of relay 1 to battery and ground, thereby operating relay 1. At the same time, battery will be removed atthe lower contact of key K from conductor 67 and will prevent any energization of the relays 9, 8, 6, 4 and 2. Upon the operation of relay 1, conductors 23 and 24 will be connected directly to conductors 25 and 26 over the contacts of relay 1 and none of the series resistance elements, such as '7', or 7", will be included serially in the input circuit of the amplifier. Due to the fact that none of the relays 9, 8, 6, 4 and 2 are operated, the shunt path, including the shunt resistances 73,, 7' r 1, and 1', will be open and none of ese resistance elements or the other series resistance will be bridged across the input of the amplifier A Underthese conditions the amplifier A will operate in the normal manner, irrespective of the artificial line N With the key K closed, as shown, battery is applied over its lower contact to the conductor 67 and thence in parallel to the windings of relays 9, 8, 6,4 and 2, placing them in astate ready to be energized u on the grounding of conductors 9, 8, 6', f and 2 respectively. Conductor 66 will also be connected to conductor 1. If ground is now applied through the master relays to conductor 1 the relay 1 will operate and contime maintaining relay 1 energized. Upon" the operation of relay 2, the shunt circuit,

including shunt resistances r r r r, and r will be closed and will be bridged at points and 21 across the conductors 62 and 6;. Under these conditions all of the resistance elements, both series and shunt, will be bridged across conductors 23, 24 and 25, 26, or in other words across the input circuit of the amplifier A thereby tending to diminish the gain of the amplifier. The op eration of the switch S and the master relays will next cause ground to be applied to conductor 3. This will operate relay 3 and at the same time maintain relay 2 energized. Under these conditions conductors 23, 24 will be connected to conductors 25, 26 through the resistance elements 1' r',, r, and 1", over the contacts'of relay 3. In other words these last mentioned series resistances will be included serially in the input circuit of the amplifier. The shunt resistance across the input of the amplifier however will be reduced as these last mentioned elements are now connected serially therein. Accordingly, under these conditions, we will have a slight decrease from the full shunt resistance of the artificial line acrossthe input circuit and a portion of the series resistance included in the input circuit. This will tend to further decrease the gain of the repeater .in the direction from line L to L The switch S will next apply ground to conductor 4, thereby operating relay 4 and at the. same time maintain relay 3 energized. Upon the operation of relay 4 a short circuit will be closed about resistance r Accordingly, this will reduce the shunt resistance across the input circuit of the amplifier and tend to further decrease the gain'of the amplifier. The switch S and the master relays would next apply ground to conductor 5, thereby operating relay 5 and maintaining relay 4 energized. Under these conditions the Series resistance elements r 1",, r", and r" would be included serially in the input circuit of amplifier'A together with the resistances 1' 9",, r'fl/and 1"", instead of being connected in shunt across said input circuit as before. This would tend to further decrease the gain of the amplifier. The switch S and the master relays would in like manner operate in sequence the relays 6, 7, 8 and 9, thus continuing to alternately decreasethe shunt resistance across the input path of the amplifier and to increase the series resistance in the amplifier to gradually decrease the ga1n thereof.

It is pointed out that an advantageous.

feature of these arrangements consists in the fact that the variable artificial lines N and N are so constructed of series and shunt resistances that when the attenuation loss is varied, nevertheless the variation in the impedance of one of these lines presented to the circuit in either direction remains practically constant. This feature is obtained in the heretofore described arrangenents by first increasing the series elements second decreasing the shunt elements, third increasing the series elements, and fourth further decreasing the shunt elements. The first and third changes increase the impedance of the artificial line, while the second and fourth decrease it, so that the changes in attenuation are obtained by a relatively simple switching arrangement but without bringing about wide variations in impedance.

Let it be assumed that switch S is resting on contact 50. This would close a circuit from ground through switch S, contact 50, winding or,relay 50,.over conductor 52 to battery and ground, thereby energizing relay 50. The energization of relay 50 would apply ground to conductor 1 over the contact and armature of relay 50 and conductor 51. When the switch S moved to contact 49 relay 49 would, in like .manner, be energized and apply ground to conductor 1. Upon touching contact 48 theswitch S would cause relay 4S to be energized. This would apply ground to conductor 1 and as soon as the switch left the conductor 49 would cause ground to be applied from the lefthand contact of relay 49,-over the righthand contact of relay 48, to conductor 2. \Vhen the switch S moves to contacts-47 ground willv still he applied'over the lefthand contact of relay 47 to conductor 1 and ground will also be applied over the right-hand contact of said relay to conductor 2. hen the switch S rests on contact 46, relay 46 will operate and apply ground to conductor 3 over its left-hand contact and apply ground to conductor 2 over its right-hand contact, thereby maintaining both the relays 2 and 3 energized at the same time. hen the switch S touches contact 45 relay 45 will operate and apply ground over its right-hand contact to conductor 2 and over its left-hand contact to conductor 3. When the switch S touches contact 44, relay 44 will operate. This will apply ground over its left-hand contact to conductor 3 and over its right-hand front contact to conductor 2' and over its right-hand back contact of conductor 4', thereby maintaining relays 2, 3 and 4 inan energized condition. In a similar manner the switch llO S, by moving along the remaining contacts, will operatethe master relays in sequence and will operate the relays of the artificial line in numerical order. As has been pointed out, this Will alternately add series resistance elements to the input circuit and cut out the resistance elements connected in shunt across said circuit and will thus gradually decrease the gain of the amplifier.

To control the gain of the repeater in the direction from line L to L the pilot circuit is also included in the same cable or subject to the same conditions as the line L The pilot circuit, as heretofore described, would control switch S, which would cooperate with the contacts 50 to inclusive to control the master relays, which in turn would control the relays 1 to 9 inclusive to change the resistance elements of the line N which would be included in the input circuit of amplifier A As this operation would be substantially the same as that heretofore described with respect to the artificial lineN no further description thereof will be given.

The conductors 1, 2', 3, 4: 5, 6', 7, 8' and 9 may be multipled to other relays similar to relays 1 to 9 inclusive to control other artificial lines or transmission vary means to control the gain of other repeaters used.

on lines which are subject to thesame variations as the pilot circuit L While the invention hasbeen disclosed as embodied in certain specific arran ements which are deemed desirable it is un erstood that it is capable of embodiment in other and different formsrwithin the spirit and scope of the appended claims. The arrangements of the invention, for example, might equally well be associated with a cord circuit repeater rather than a through line repeater set.

What is claimed isz 1. In a signaling system, a plurality of transmission circuits subject to similar y'ariations in their electrical characteristics, one of said circuits being a pilot circuit, means associated with said pilot circuit responsive to changes in the electrical characteristics thereof, and means controlled by said responsive means for varying the characteristics of the other circuits in accordance with the variations in the characteristics of said pilot circuit, said last mentioned means comprising a transmission varying device.

2. In a signaling system, a plurality of transmission circuits subject to similar variations in their electrical characteristics,

one of said circuits being a pilot circuit, a telephone repeater in one of said circuits.

means in said pilot circuitresponsive to changes in the electrical characteristics thereof, and a variable artificial line associated with the input of said telephone repeater controlled by said responsive means for varying the characteristics of said repeater circuit in accordance with the variationsin the characteristics of said pilot cir- .cuit.

3. In a signaling system, a plurality of transmission circuits including repeater apparatus, a pilot circuit subject to influences similar to those affecting the transmission efliciency of said transmission circuits,

switching means, means to automatically set said switching means in accordance with the electrical condition of said pilot circuit, transmission varying devices associated with said repeater apparatus, and means con- {rolled by said switching means for control- 111g whereby the gain of said repeater apparatus may be varied.

4. In a signaling system, a plrrality of transmission circuits including repeater apparatus, a pilot circuit subject to influences similar to those affecting the transmission efliciew of said transmission circuits, switching means, means to automatically set said switching means in accordance with the electrical condition of said pilot circuit, variabl'e artificial lines associated with said repeater apparatus, relays for controlling said artificial lines, and a set of master relays controlled by said switching means for controlling said relays.

5. In a signaling system, a plurality of transmission circuits including repeater apparatus, a'pilot circuit subject to influences similar to those affecting the transmission efliciency of said said transmission circuits,

switching means, means to automatically set said switching means in accordance with the electrical condition of said pilot circuit, variable artificial lines associated with the input circuits of said repeater apparatus and comprising a plurality of series and shunt resistances, relays for closing shunts about certain of said resistance elements whereby the amount of series and shunt resistance associated with said repeater input circuits may be varied, and a set of master relay controlled by said switching meansfor co :trolling said relays.

In testimony whereof, we have signed our names to this specification this 11th day of September, 1923.

HARRY NYQUIST. LEWIS L. BOUTON. HUGH F. SHOFFSTALL,

said transmission varying devices 

